Cathode ray tube having an electrostatic accelerating lens

ABSTRACT

A tube envelope having a neck portion, a faceplate carrying a target electrode, and a large-diameter portion disposed between the neck portion and the target electrode and joined to the neck portion at an intermediate point along the length thereof so that a part of the neck portion extends into the space enclosed by the large-diameter portion, the tube being provided with an accelerating lens system composed of a first electrode disposed in the neck portion and a second electrode disposed in the largediameter portion, with the first and second electrodes overlapping one another in the direction of the tube axis and the second electrode being disposed closer than the first electrode to the target electrode.

United States Patent [72] Inventors Klaus Schaffernicht Traminerweg; Adolf Eckert, Ulm(Danube), Germany [21] App1.No 611,274 [22] Filed Jan. 24, 1967 [45] Patented Mar. 9, 1971 [73] Assignee Telefunken Patentverwertungsgesellschaft m.b.ll. Ulm (Danube), Germany [32] Priority Jan. 28, 1966, Mar. 3, 1966 [33] Germany [3 1 T30344 and T30571 [54], CATHODE RAY TUBE HAVING AN ELECTROSTATIC ACCELERATING LENS 16 Claims, 6 Drawing Figs.

[52] U.S.Cl 315/16, 313/82, 313/85, 313/290, 313/313 [51] Int. Cl ..l-l01j 29/46, H01 j 29/56 [50] Field ofSearch 313/82- (B.F.C.Digest), 82 (orig.); 313/87, 82; 313/85;

[56] References Cited UNITED STATES PATENTS 2,975,315 3/1961 Szecho 313/82 3,375,390 3/1968 Schlesinger 313/83 2,178,973 11/1939 Schoenberg et a1.. 313/82 3,023,336 2/1962 Frenkel 3 l3/84X Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Attorney-Spencer & Kaye ABSTRACT: A tube envelope having a neck portion, a faceplate carrying a target electrode, and a large-diameter portion disposed between the neck portion and the target electrode and joined to the neck portion at an intermediate point along the length thereof so that a part of the neck por-- imlmmmlllzymawz V I PATENTEDHAR 91971 34569772 samluFz Inventors Klaus Scfia'efermfihi AdolF Eckerr BY M r/ AHm-nevs EATI'TODE RAY TUBE HAVING AN ELECTROSTATIC AEQELERATING LENS BACKGROUND OF THE INVENTION The present invention relates to a cathode ray tube, and particularly to a cathode ray tube providing improved protection against sparkovers.

The evacuated envelope of a cathode ray tube having a target electrode in the form of either a fluorescent screen or a large-surface energy storage electrode is generally composed os a substantially cylindrical neck portion, a large-diameter portion, which is often identified as a cone portion although it is not necessarily conical, having a diameter which increases to be equal in size to the target electrode, and a faceplate which is generally in the form of a plane or slightly curved window and which carries the target electrode. The individual portions are generally made of glass and are fused together. The large-diameter portion has one end fused to that end of the neck portion which is nearest the target electrode and its other end fused to the face plate.

For achieving high acceleration of the beam electrons, it is the general practice to provide the large-diameter portion with a high-potential electrode which generally consists of an electrically conductive layer sprayed or painted on, or otherwise attached, to its inner wall. It is known that during the operation of such tubes electrical sparkovers occasionally occur, i.e., from the layer having a high voltage of several kilovolts to a low-potential electrode of the electrode system.

For certain applications of such tubes it is absolutely necessary that the occurrence of such sparkovers be completely prevented. For example, transistorized circuits are extremely sensitive to excessive voltage surges and electrical sparkovers in the cathode ray tube associated with such a circuit arrangement could lead to the destruction of an entire circuit portion.

It is therefore an object of the present invention to prevent such sparkovers from occurring.

Another object of the present invention is to insulate the electrodes of an accelerating lens system from one another so as to prevent the occurrence of such sparkovers.

A further object of the present invention is to provide an accelerating lens system having high refraction power and capable of providing improved focusing.

SUMMARY OF THE INVENTION These and other objects according to the present invention are achieved, in a cathode ray tube having an envelope which includes a hollow neck portion of small diameter, a faceplate carrying a target electrode, and a large-diameter portion having one end joined to the neck portion and its other end equal in diameter to the face plate and joined to the faceplate, by the improvement wherein the large-diameter portion is joined to the neck portion at an intermediate location therealong, which location is spaced from that extremity of the neck portion which is nearest the target electrode. As a result, part of the neck portion will extend into the space enclosed by the large-diameter portion.

According to another feature of the present invention, the cathode ray tube is provided with an accelerating lens system composed of a first annular electrode disposed within the neck portion, at least part of this first electrode being disposed in that part of the neck portion which extends into the space enclosed by the large-diameter portion, and a second annular electrode disposed within the large-diameter portion.

Tubes constructed according to the present invention are well suited for use in systems in which a first image-forming lens, disposed in the path of the electron beam produced by an electron gun, produces an intermediate image of the cross section of a selected point along the beam and in which the accelerating leans according to the present invention, which is also disposed in the path of the beam and downstream of the first lens, serves to reproduce such intermediate image on the target electrode. Arrangement of this type, and their advantages, have been disclosed in copending U.S. Application Ser. No. 482,533, filed by Klaus Schafiemicht on Aug. 25th, 1965, and assigned to the same assignee as the present application. This application is now abandoned and was reflled as a Streamlined Continuation Application, Ser. No. 785,049, on Dec. 12th, 1968.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified cross-sectional view of an evacuated envelope of a cathode ray tube according to the present invention.

FIG. 2 is a view similar to that of FIG. 1 of another evacuated envelope of a cathode ray tube according to the present invention.

FIG. 3 is a diagrammatic side view of the beam deflecting and focusing system of a cathode ray tube according to the present invention.

FIG. 4 is a cross-sectional view of a portion of another embodiment of a cathode ray tube system according to the present invention.

FIG. 5 is a cross-sectional view of a portion of a cathode ray tube system according to the present invention.

FIG. 6 is a cross-sectional view of a portion of a further preferred embodiment of a cathode ray tube system according to the present invention. 3

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cathode ray tube of the type which may be used as a television picture tube and which includes an evacuated envelope having a neck portion 1 and a flared funnelshaped portion 2 closed by .a faceplate carrying the fluorescent screen 4. An electrically conductive layer 3 is applied, in a known manner, to the inner wall of the flared portion 2. A'lead-in contact 5 passes through portion 2 and is electrically connected to the high-voltage conductive layer 3. The neck portion 1 is provided, in a known manner, with plug prongs 6 at its outer end and contains the various electrodes of an electron gun as well asfurther electrodes for the beam deflection, these elements being well-known in the art and not being illustrated for purposes of simplicity.

The inner end 8 of the neck portion 1, which faces toward the fluorescent screen 4, extends into the portion 2 to a certain extent. The fused joint 7 between the portion 2 and the neck portion 1 is disposed at a distance from the neck portion end 8 facing the fluorescent screen. The high-voltage layer 3 is preferably of sufficient extent that the end 9 thereof which is furthest removed from screen 4 extends beyond, or overlaps, the end 8 of the tube neck in the direction of the tube axis.

FIG. 2 shows an oscillograph tube constructed according to the present invention. The evacuated envelope of the tube consists of a neck portion 11, a body portion 12 and a faceplate carrying a fluorescent screen 14. The neck portion 11 has an inner end 18 extending toward screen M and an outer end carrying plug prongs 16. The fused joint 17 between the body portion 12 and the neck portion 11 is spaced behind the extremity 'of end l8 so as to be further away from screen 14 than is that extremity.

The electrically conductive layer 13, which is electrically connected to contact l5, extends to a. point 19 which is also behind the extremity of end 118 so that a suitable overlapping exists between the layer 13 and the end 18 of the tube neck in the direction of the tube axis. In such a tube, the layer 13 produces the effect of an electron-accelerating lens.

In the embodiment shown in FIG. 2, the diameter of the end 18 of the tube neck is somewhat smaller than the diameter of the external portion of the tube neck 11. This helps to simplify fusion at joint 17 and to permit the individual parts to be manufactured to greater tolerances. Furthermore, such an arrangement can offer certain electron-optical advantages, particularly when the ratio of the diameter of the layer T3 to the diameter of an electrode disposed within the neck is given an optimum value. Advantageously, an electrode connected to have a low positive potential and having a hollow cylindrical ihape, may be disposed within the neck portion end 18 so as to .oooerate with the layer 13, which is placed at a high positive potential, to forman accelerating lens, This lens can possess a very high refractive power with high field strength as a result of the novel construction of the evacuated envelope of the tube according to the invention. Such an accelerating leans is particularly well suited, because of its high refraction power, for recreating an intermediate image of an electron beam cross'section which has been generated by a first image-forming lens. Systems capable of creating such intermediate images have already been described in the above-mentioned U.S. Application Ser. No. 785,049.

FIG. 3 schematically shows a beam deflection and focusing in a cathode ray tube for forming such an intermediate electron beam image. By means of a conventional electron gun 51, an electron beam 59 having a crossover point 52 at some distance from the gun is generated. A first image-forming lens 53 serves to form an intermediate image 56 of the beam crossover point 52, which image is recreated, or focused with the aid of the accelerating'lens 57, on a'fluorescent screen 58. The image 56 is relatively far from screen 58. The beam deflection means, which in the illustrated embodiment are constructed as electrostatic pairs of deflector plates 54 and 55, are suitably disposed between the image-forming lens 53 and the accelerating lens 57. It has been found to be particularly desirable that the cross section of the intermediate image 56 be equal in size to that of the beam crossover point 52, of which it is an image. The intermediate image can also be of somewhat smaller size than the beam crossover point 52. For the tube to have a high deflection sensitivity, care should be taken, however, that .the intermediate image 56 not be more than twice the size of the beam crossoverpoint 52. Since the lens 57 is constructed as an accelerating lens, the resulting tube will have an improved deflection sensitivity and will be capable of producing a picture which is more sharply focused and which has increased brightness.

FIG. 4 shows a preferred embodiment of a cathode ray tube which, in the present case, consists of an oscillograph tube having a neck portion 411, a funnel-shaped portion 423, and a large-diameter portion 415 terminating in a faceplate 416 which carries a fluorescent screen 417. The electron gun, 51 (FIG. 3) which can be constructed in a conventional manner, is not shown in FIGS. 4 to 6. The first image-forming lens, 53 (FIG. 3) well-known per se, is also not illustrated in FIG. 4 to 6. The electron gun is preferably of a type which generates a beam having a crossover pint at not too great a distance from the emission area of the cathode-A real image of a cross section of the electron beam generated by the electron gun, and preferably of the cross section of the beam crossover point, is formed by the first image-forming lens 53, as can be seen in FIG. 3, in a plane intersecting the region of influence of the accelerating lens 57 (FIG. 3).

The first image-forming lens may consist of a conventional electron lens as, for instance, a so-called unit lens, or of an accelerating lens. A unit lens consists, as is known, essentially of three annular or tubular electrodes disposed in succession along the beam path, with the middle electrode being maintained at a lower potential than the two adjoining electrodes.

Following the first image-forming lens it is advisable to have deflection means which, in the embodiment shown in FIG. 4, consist of two pairs of deflection plates 412 and 413 disposed at right angles to each other. In place of these pairs of deflector plates, electromagnetic deflector coils may be provided and disposed in a conventional manner at the desired location on the outside periphery of the neck portion 411.

The second, or accelerating, lens serves, according to the invention, to recreate, or focus, the intermediate electron image created by the first image-forming lens on the fluorescent screen 417. This accelerating lens is constituted by the two electrodes 421 and 418. It has been found to be advisable to form the second electrode 418, which is to be placed at a higher potential than electrode 421 as an electrically conductive layer on the inside wall of tube portion 415.

A lead-in 419 serves to apply the desired potential to the second electrode 418.

Such an accelerating lens has been found to possess-a very high refractive power which improves the deflection sensitivity of the tube, the focusing of the beam on the fluorescent screen, and the brightness of the resulting display, or picture.

It is advisable to construct the two electrodes 421 and 418 of the accelerating lens in axial symmetry. The'first electrode 421 can, if required, be provided with annular or hood-shaped projecting flanges. It is also possible to elongate the second electrode 418 somewhat in the direction of the cathode, or electron gun, so that it also totally or partially covers the conical part 423 of the tube envelope.

According to a preferred form of construction of embodiments of the present invention, the arrangement shown in FIG. 4 is such that the screenward end 420 of the tube neck 411 extends somewhat into the region enclosed by the largediameter portion 415 of the tube wall and surrounds the first electrode 421 for most of the length of the latter. Such a form of construction of the tube permits the accelerating lens to have a very high refractive power associated with a very high electric field strength. It is further advantageous to have the screenward end of the first electrode 421 overlap the cathode end 422 of the second electrode 418 in the general direction of beam travel. To achieve a particularly good electric field strength, the cathode end 422 of the electrode 418 and the screenward end 420 of the neck portion should also overlap. At this point it should be mentioned that the tube portions 411, 423 and 415 are made of a good electrical insulating material, preferably glass.

.According to anotherfeature of the present invention, a further electrode 414 is disposed ahead of the accelerating leans, in the direction of travel of the beam electrons, which further electrode is preferably axially symmetrical and may be constituted by, for instance, an annular metal body. This further electrode 414 is placed at a potential which is more positive than the potential of the first electrode 421.

The purpose of the furtherelectrode 414 is asfollows: It was pointed out above that the accelerating lens, consisting of electrodes 421 and 418, is to have a very high refractive power. This means that a very high potential difference should exist between these two electrodes. In order to, for example, double the total refractive power, one can either double the potential of the second electrode 418 or halve the potential of the first electrode 421. The latter is more suitable inasmuch as the required absolute voltages can then be created much more easily. It is, for instance, much easier to generated a high voltage of only 20 kv. than a high voltage of 40 kv. However, the potential of the first electrode 421 can not be selected at any desired low value because if this potential were made too low the electrode 421 would no longer be able to attract the beam electrons and the electron beam cross section would thus be unfavorably influenced.

This drawback is eliminated, according to the present invention, by applying to the further electrode 414 a voltage which sufiices to assure sufficient attraction of the beam electrons. Thus, the further electrode 414, relieves the electrode 421 of the task of attracting the beam electrons, so that the first electrode 421 can be maintained at the desired low voltage level, thus permitting the refractory power of the accelerating lens to be increased in a simple manner.

In order that the quality of the image formed on the fluorescent screen by the accelerating lens is not diminished, care must be taken so that the potential difference between the electrodes 414 and 421 is substantially lower than the potential difi'erence between the electrodes 421 and 418. In other words, the refractory power of the lens defined by the electrodes 414 and 421 should be negligible in comparison with the desired refractory power of the accelerating lens defined by the two electrodes 421 and 418.

A numerical example of the voltages which may be employed in an embodiment of the present invention will now be given. This example will demonstrate that the required conditions described above can easily be fulfilled in practice. During operation of the tube, a DC voltage of 500 v. was applied to the electrode 414, a DC voltage of 250 v. was applied to electrode 421, and a DC voltage of 25 kv. was applied to electrode did. The voltage ratio between electrode 421 and elecnode 422% is therefore 1:100. The voltage ratio between electrode 4M and electrode 423 is 2:1. Thus, the difference between the two refractive powers is so large that the refractive power of the lens defined by electrodes 4M and 32T can be ignored for all practical purposes. All voltages applied are DC voltages. The sources of voltage potential are shown schematically in H68. 4 and 6.

The potential applied to the first electrode 321 further exerts an influence on the geometric distortion of the picture appearing on screen 417 so that a suitable selection of this potential can serve to correct such geometric distortions. It is of further advantage that the potential drop created by the lower potential applied to the electrode 421 serves to at least trap the slow secondary electrons which might be generated upon impact of the beam on the pairs of deflector plates 412 and M3 in order to prevent an undesired brightness, or glow, from appearing on the screen.

FIG. 5 shows a further embodiment of a cathode ray tube according to the invention of which only part of the neck portion 34! and part of the large-diameter portion 31 are shown. The accelerating leans is formed by the two electrodes 34 and 32. The second electrode 32 is constituted by a conductive layer applied to the inner wall of the tube.

The inner end 33 of the neck portion 30, which end is furthest removed from the cathode, extends into the region enclosed by the large-diameter portion 31 and, as can be seen in the drawing, has a diameter which is somewhat smaller than that of the remainder of the neck portion. Within this reduced-diameter end portion 33 of neck portion 30, the first electrode 34 of the accelerating lens is disposed and is connected to a source of a relatively low potential. in this embodiment, this first electrode 34 is preferably applied to the inner wall of the neck end portion 33 in the form of a conductive layer. This first electrode 34, however, can also be constituted by an annular, or tubular, metal electrode similar to the electrode 421 of H6. 4. Disposed ahead of the first electrode 34, with respect to the direction of travel of beam electrons, is a further electrode 35 which serves the .same purpose as the further electrode 414 of FIG. 4.

The cathode end 36 of the second electrode 32 overlaps, in the direction of the tube axis, the end of portion 33, which portion extends into the space enclosed by large-diameter portion 31. it is advisable that the electrode 34 also overlap the electrode 32 in the direction of the tube axis.

Preferably, the electrodes 32 and 34 of the accelerating lens are constructed to be axially symmetrical. It is also advantageous to construct the first image-forming lens to be axially symmetrical.

HG. a shows a further preferred cathode ray tube according to the present invention. The evacuated envelope consists of a neck portion 6i and a large-diameterportion 63 having a funnel-shaped part. A fusion joint 67 is formed between the neck portion hi and the largediarneter portion 63. The accelerating lens consists of a first electrode es and an electrically conductive layer 6? applied to the inner wall 69 of portion 63. The first electrode as is disposed within the reduceddiameter part oz of neck portion iii and is provided with a flanged border at the end directed toward the fluorescent screen. A further electrode 64 is disposed, in the direction of travel of the beam electrons, ahead of the first electrode 65. This further electrode serves the same purpose as the electrode 414 of the embodiment of FIG. 4. This embodiment is particularly well suited for an oscillograph tube provided with electrostatic deflector plates and employing intermediate image forming, as described in connection with FIG. 3. The two pairs of deflecto? plates are shown at 71 and 72.

it has been found that cathode ray tubes constructed according to the present invention, so that their neck portion extends partially into the space enclosed by the large-diameter portion, exhibit an excellent resistance to sparlrovers. Experiments have shown, for example, that even when acceleration voltages as high as 30 to 40 kv. are employed, such sparkovers are completely prevented even when the tube is subjected to extreme operating conditions.

A further significant advantage of the present invention resides in the fact that embodiments thereof are relatively simple to manufacture and are no more expensive to fabricate than prior art tubes.

Whereas it has been the usual practice to fuse the end of the neck portion to the large-diameter portion of the evacuated envelope, fabrication of embodiments of the present invention may be carried out by fusing the large-diameter envelope portion to the neck portion at a point spaced some distance from the inner extremity of the neck portion. in the manufacture of tubes according to the present invention, it has been found to be advantageous tocarryl out this fusion operation as the last assembly step and to evacuate the tube on a pump stand. Thus, the neck portion containing the electrode system is separately manufactured, as is the subassernbly of the largediameter envelope portion, the faceplate and the target electrode, and these two asse'mbled parts are then fused together in the last fabrication operation.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. In a cathode ray tube having an envelope which includes a hollow neck portion of small diameter, a faceplate carrying a target electrode, and a large-diameter portion having one end joined to said neck portion and its other end equal in diameter to the size of said faceplate and joined to said faceplate, wherein said large-diameter portion is joined to said neck portion at an intermediate location therealong, which location is spaced from that extremity of said neck portion which is nearest said target electrode so that part of said neck portion extends into the space enclosed by said large-diameter portron;

the improvement wherein an electrostatic accelerating lens of high refractory power is disposed in said tube, said accelerating lens including a first tubular electrode disposed within said neck portion at least partially within the part thereof which extends into the space enclosed by said large-diameter portion, and a second annular electrode disposed within said large-diameter portion;

wherein a further tubular electrode is disposed in said envelope at a location which is further away from said target electrode than is said first electrode;

wherein said cathode ray tube further comprises: an electron gun for producing an electron beam which is directed toward said target electrode; and an image-forming lens disposed in said tube in the path of the electron beam produced by said gun for producing an intermediate image of the cross section of a selected point along such beam; and,

wherein said accelerating lens and said further tubular electrode are disposed in the path of such beam and downstream of said image-forming lens, with respect to the direction of travel of the beam electrons, for reproducing such intermediate image on said target electrode.

2. An arrangement as defined in claim further comprising means for placing said first electrode at a predetermined potential, for placing said further electrode at a higher potential than said first electrode, and for placing said second electrode at a higher potential than said first electrode.

3. An arrangement as defined in claim 2 wherein the potential difference between the voltages appearing on said first and further electrodes is less than the potential difference between the voltages applied to said first and second electrodes.

4. ln a cathode ray tube having an envelope which includes a hollow neck portion of small diameter, a faceplate carrying a target electrode, a large-diameter portion having one end oined to said neck portion and its other end equal in diameter to the size of said faceplate and joined'to said faceplate, and an electron gun means for producing an electron beam which is directed toward said target electrode:

An image-forming lens means, disposed in said tube in the path of the electron beam produced by said gun means, for producing an intermediate image of the cross section of a selected point along such beam; and

an electrostatic accelerating lens means of high refractory power arranged between said gun and said target electrode in the path of such beam and, with respect to the direction of travel of the beam electrons, downstream from said image-forming lens means, said electrostatic accelerating lens means having a function of reproducing such intermediate image on said target electrode and comprising, in the spatial order from said gun means toward said target electrode, a further tubular electrode disposed in the neck portion, a first tubular electrode disposed at least partially within the neck portion, and a second annular electrode.

5. An arrangement as defined in claim 4, further comprising a means for placing said first electrode at a predetermined potential, for placing said further electrode at a higher potential than said first electrode, and for placing said second electrode at a higher potential than said first electrode.

6. An arrangement as defined in claim 5, wherein the potential difference between the voltages appearing on said first and further electrodes is less than the potential difference between the voltages applied to said first and second electrodes.

7. An arrangement as defined in claim 1 wherein said image-forming lens is arranged to'fonn an intermediate image of the crossover point of such beam.

8. An arrangement as defined in claim 1 further comprising deflection means disposed in the path of such electron beam between said image-forming lens and said further tubular electrode for deflecting such beam across said target electrode.

9. An arrangement as defined in claim 4 wherein said second electrode is in the form of a layer of electricallyconductive material disposed on the inner wall of said largediameter portion.

10. An arrangement as defined in claim 4 wherein said first electrode is constituted by a cylindrical metal body.

11. An arrangement as defined in claim 4 wherein said first electrode is constituted by a layer of electrically conductive material disposed on the inner wall of said neck portion.

12. An arrangement as defined in claim 4 wherein said first and second electrodes overlap in a direction along the axis of said tube.

13. An arrangement as defined in claim 4 further comprising electron beam deflection means disposed in said envelope, and wherein said accelerating lens is disposed between said deflection means and said target electrode.

14. An arrangement as defined in claim 4 wherein said image-forming lens is arranged to form an intermediate image of the crossover point of such beam.

15. An arrangement as defined in claim 4 further comprising deflection means disposed in the path of such electron beam between said image-forming lens and said accelerating lens for deflecting such beam across said target electrode.

16. An arrangement as defined in claim 4 wherein said target electrode is constituted by a fluorescent screen. 

1. In a cathode ray tube having an envelope which includes a hollow neck portion of small diameter, a faceplate carrying a target electrode, and a large-diameter portion having one end joined to said neck portion and its other end equal in diameter to the size of said faceplate and joined to said faceplate, wherein said large-diameter portion is joined to said neck portion at an intermediate location therealong, which location is spaced from that extremity of said neck portion which is nearest said target electrode so that part of said neck portion extends into the space enclosed by said large-diameter portion; the improvement wherein an electrostatic accelerating lens of high refractory power is disposed in said tube, said accelerating lens including a first tubular electrode disposed within said neck portion at least partially within the part thereof which extends into the space enclosed by said largediameter portion, and a second annular electrode disposed within said large-diameter portion; wherein a further tubular electrode is disposed in said envelope at a location which is further away from said target electrode than is said first electrode; wherein said cathode ray tube further comprises: an electron gun for producing an electron beam which is directed toward said target electrode; and an image-forming lens disposed in said tube in the path of the electron beam produced by said gun for producing an intermediate image of the cross section of a selected point along such beam; and wherein said accelerating lens and said further tubular electrode are disposed in the path of such beam and downstream of said image-forming lens, with respect to the direction of travel of the beam electrons, for reproducing such intermediate image on said target electrode.
 2. An arrangement as defined in claim further comprising means for placing said first electrode at a predetermined potential, for placing said further electrode at a higher potential than said first electrode, and for placing said second electrode at a higher potential than said first electrode.
 3. An arrangement as defined in claim 2 wherein the potential difference between the voltages appearing on said first and further electrodes is less than the potential difference between the voltages applied to said first and second electrodes.
 4. In a cathode ray tube having an envelope which includes a hollow neck portion of small diameter, a faceplate carrying a target electrode, a large-diameter portion having one end joined to said neck portion and its other end equal in diameter to the size of said faceplate and joined to said faceplate, and an electron gun means for producing an electron beam which is directed toward said target electrode: An image-forming lens means, disposed in said tube in the path of the electron beam produced by said gun means, for producing an intermediate image of the cross section of a selected point along such beam; and an electrostatic accelerating lens means of high refractory power arranged between said gun and said target electrode in the path of such beam and, with respect to the direction of travel of the beam electrons, downstream from said image-forming lens means, said electrostatic accelerating lens means having a function of reproducing such intermediate image on said target electrode and comprising, in the spatial order from said gun means toward said target electrode, a further tubular electrode disposed in the neck portion, a first tubular electrode disposed at least partially within the neck portion, and a second annular electrode.
 5. An arrangement as defined in claim 4, further comprising a means for placing said first electrode at a predetermined potential, for placing said further electrode at a higher potential than said first electrode, and for placing said second electrode at a higher potential than said first elecTrode.
 6. An arrangement as defined in claim 5, wherein the potential difference between the voltages appearing on said first and further electrodes is less than the potential difference between the voltages applied to said first and second electrodes.
 7. An arrangement as defined in claim 1 wherein said image-forming lens is arranged to form an intermediate image of the crossover point of such beam.
 8. An arrangement as defined in claim 1 further comprising deflection means disposed in the path of such electron beam between said image-forming lens and said further tubular electrode for deflecting such beam across said target electrode.
 9. An arrangement as defined in claim 4 wherein said second electrode is in the form of a layer of electrically conductive material disposed on the inner wall of said large-diameter portion.
 10. An arrangement as defined in claim 4 wherein said first electrode is constituted by a cylindrical metal body.
 11. An arrangement as defined in claim 4 wherein said first electrode is constituted by a layer of electrically conductive material disposed on the inner wall of said neck portion.
 12. An arrangement as defined in claim 4 wherein said first and second electrodes overlap in a direction along the axis of said tube.
 13. An arrangement as defined in claim 4 further comprising electron beam deflection means disposed in said envelope, and wherein said accelerating lens is disposed between said deflection means and said target electrode.
 14. An arrangement as defined in claim 4 wherein said image-forming lens is arranged to form an intermediate image of the crossover point of such beam.
 15. An arrangement as defined in claim 4 further comprising deflection means disposed in the path of such electron beam between said image-forming lens and said accelerating lens for deflecting such beam across said target electrode.
 16. An arrangement as defined in claim 4 wherein said target electrode is constituted by a fluorescent screen. 